1. Field of the Invention
The invention relates in general to the method and apparatus for positioning a scanning starting point of an image scanning apparatus, and more particularly to the method and apparatus for positioning a scanning starting point by utilizing multiple reference points to achieve high precision.
2. Description of the Related Art
In the multimedia age, image scanners are commonplace for users. The demand for high scanning quality and speed are increasing as well. The way to enhance the scanning speed is to make the image-capturing carriage move quickly and efficiently from its resting position to the scanning starting point to proceed the scanning. Conventionally, the methods for positioning a scanning starting point to initiate the image scanning are as follows:                (a) Referring to FIG. 1, Taiwan Patent Publication No. 147499 discloses that the reference point P for positioning is a corner of a reflecting area 12. The relative position between the reference point P and the scanning starting point Q is regulated before the product leaves the factory. After the position of the reference point P is determined, the carriage can then obtain the position of the scanning starting point Q. In this way, the carriage can move to the scanning starting point Q and proceed to scan.        (b) Referring to FIG. 2, Taiwan Patent Publication No. 338868 discloses that a mark 22 is used for positioning. After getting any two reference points P1 and P2 of the mark 22, the position of the scanning starting point Q can be obtained by the two reference points P1 and P2 according to the coordinates, functional relation, mark, and pre-determined length of the scanning starting point.        
In the above cases, a scanning starting point is used as a starting position for the scanning carriage, however, the actual contents may not be exactly at the scanning starting point Q. Thus, in these cases, the carriage needs to traverse the distance between the scanning starting point Q and the actual contents of the document. Errors may occur during this due to the unsteady transmittal speed of the carriage, mechanical errors among transmission components, or transmittal errors of the carriage. Besides, the farther the actual contents are away from the scanning starting point, the larger the moving error is. Generally speaking, the moving error is around 2 mm when the carriage moves from the scanning starting point Q to the image starting point of the scanning area at a distance. This is not acceptable for high precision scanning and has become a topic that must be overcome.